Monsters peer and prowl, roar and ravage in myths and legends the world over. They are the stuff of nightmares, the looming presences outside the comforting circle of firelight, the menacing shapes glimpsed moving through the shadows of trees or in deep water. Monsters are creatures that represent everything that is fearful about the natural world and the darker corners of human nature. Mythological monsters inspire dread and embody evil. They challenge heroes and heroines to prove their worth in order to advance in their quests or simply to survive.

Types and Characteristics of Monsters. Monsters are by definition unnatural, something that should not exist. The word monster comes from the Latin monstrum, meaning a sign of future events. The Romans used the word to refer to bizarrely unusual events—such as a rain of mud or the birth of a two-headed calf—that were believed to show divine displeasure...